Heat dissipation is an important consideration in the design of power electronics and must be controlled carefully. To protect semiconductor devices against overheating, the cooling system of a power module should be very efficient. The cooling approach is typically based on the type of power module. For example, power modules can be cooled directly or indirectly. Furthermore, modules may or may not have a base plate where the base plate can be flat or structured. Conventional power module base plates are normally made of copper because of the excellent heat conductivity. Other materials like AlSiC, aluminum or clad materials are suitable substitutes with the advantage of a lower cost. Power modules without a base plate are less expensive, but with reduced thermal performance as compared to modules that use a base plate.
Power modules with and without a base plate can be cooled indirectly by an air or fluid based cooler. Typically the heat generated in the semiconductor dies (chips) flows through a ceramic substrate with metallized sides such as a DCB (direct-copper-bonded), the different solder layers (chip-soldering, system soldering, etc.) and the base plate. The thermal contact for heat conduction is realized by a thermal grease between the base plate (or DCB in the case of no base plate) and the cooler. Cooling semiconductor dies in this way is less than optimal as the thermal grease has a low heat conductivity of about 1 W/mK.
Directly cooled power modules with structured base plates provide more efficient cooling of power devices. Such base plates have pin or fin cooling structures on the bottom side of the base plate in direct contact with a cooling liquid (e.g. water, or a water glycol mixture) so that high heat transfer coefficients are achieved. Different technologies for structured base plate production are available such as metal-injection-molding process (MIM) or forging technology, which tend to have high production and material costs.